The mean absolute error (MAE) and the mean squared error (MSE) are widely used to measure the crowd counting error on different methods [1]}, [2]}, [3]}, [4]}. They are defined as follows:
\(MAE = \frac{1}{V}\sum _{i=1}^{V}\left| z_{i}- \hat{z_{i}} \right|,\) 
\(MSE = \sqrt{\frac{1}{V}\sum ^{V}_{i=1}\left( z_{i} - \hat{z_{i}} \right)^{2}}.\) 
